Disclosed herein is an aqueous ink for indirect printing applications including water; a co-solvent; a colorant; and a polymer latex comprising an aqueous dispersion of polymer particles wherein the polymer latex has a softening temperature of from about 60° C. to less than 105° C. and a glass transition temperature of from about 45° C. to about 100° C.
In direct printing machines, a marking material is applied directly to a final substrate to form the image on that substrate. Other types of printing machines use an indirect or offset printing technique. In indirect printing, the marking material is first applied onto an intermediate transfer member, and is subsequently transferred to a final substrate.
In one type of indirect printing machine, a piezoelectric ink jet print head is used to apply ink to the intermediate transfer material layer. The ink can be disposed on a liquid layer which can be in the form of a release agent, such as oil, that is capable of supporting the printed image for subsequent transfer. The intermediate image is transferred by contact between the transfer drum and the substrate, typically with the assistance of a pressure roller or drum. An exemplary indirect printing apparatus 10 is shown in FIG. 1. In this apparatus, a print head 11 directs a marking material, such as ink droplets, onto a layer 12 of intermediate transfer material to form an image 26. This transfer material layer 12 is carried by an intermediate transfer member 14, which in the illustration is a rotating drum or roller. An optional heater 19 can be provided to control the temperature of the ink image prior to contacting the substrate 28.
The substrate 28 is conveyed between the intermediate transfer member 14 and a transfer or pressure roller 22. Optional heaters 20 and 21 can be provided to pre-heat the substrate 28 to facilitate reception of the image. An optional heater 24 can be provided to heat the transfer roller 22. As the substrate is conveyed between the rotating rollers 14 and 22, the image 26 is transferred onto the substrate as image 26′. Appropriate pressure is maintained between the two rollers so that the image 26′ is properly spread, flattened, and adhered onto the substrate 28. An optional stripper 25 can be provided that assists in removing any ink remaining on the intermediate transfer member 14 prior to receiving a new ink image 26 from the print head 11.
A two step printing process, then, can comprise applying an ink in an imagewise fashion onto an intermediate receiving member such as a drum, belt, etc., using an ink jet print head. The ink wets and spreads on the intermediate receiving member to form a transient image. The ink forming the transient image can then undergo a change in properties such as partial or complete drying, thermal or photo-curing, gelating, etc., and the resulting transient image can be transferred to a final image receiving substrate.
While known ink compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions with certain characteristics. A need remains for inks, specifically inks for indirect printing systems, that are compatible with different printing subsystems including jetting and transfer subsystems, and which enable high quality printing at high speed. What is further needed is an indirect printing ink that enables and performs well in both wetting and transfer subsystems. What is further need is an indirect printing ink that displays acceptable wettability characteristics while also displaying acceptable transfer characteristics.
The appropriate components and process aspects of the each of the foregoing U.S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.